[Effects of potassium level on photosynthetic characteristics and chloroplast submicroscopic structure of muskmelon leaves].

With soilless culture in greenhouse, this paper studied the effects of three potassium (K) levels (120, 240, and 360 mg x L(-1)) on the photosynthetic characteristics and chloroplast submicroscopic structure of muskmelon cv. 'Tiantian No. 1' leaves. The results showed that at low (120 mg x L(-1)) and high (360 mg x L(-1)) K levels, the net photosynthetic rate (Pn) decreased, chloroplast lamellar structure disordered, and lamella number decreased. No significant effects were observed on CO2 compensation point (70 microl x L(-1)), saturation CO2 for photosynthesis (600 microl x L(-1)) and light compensation point (50 micromol x m(-2) x s(-1)) at the three K levels. The saturation light for photosynthesis, carboxylation efficiency and apparent quantum yield at 240 mg x L(-1) K level were significantly higher, being 1200 micromol x m(-2) x s(-1), 0.1364 and 0.0237, respectively. Under the conditions of this study, the optimal K level in the nutrient solution for muskmelon soilless culture was 240 mg x L(-1).